The invention relates to a blown lamp bulb with a glass wall comprising
a substantially parabolically curved wall portion with a focus, and PA0 a neck-shaped wall portion extending from the apex of said parabolically curved wall portion to the exterior.
The bulb has a largest diameter transverse to the axis of symmetry.
The focus of the parabolically curved wall portion is located between said largest diameter and said neck-shaped wall portion near the neck-shaped wall portion. The ratio between the largest diameter and the focal distance is between 4 and 9.
A curved wall portion is opposite to said neck-shaped wall portion and said parabolically curved wall portion.
Electric incandescent lamps having such a blown lamp bulb are generally known and are commercially available. An embodiment of such an electric incandescent lamp is known, for example, from European Patent Specification No. 0 022 304 B1.
In the known lamp, the parabolically curved wall portion is provided with a mirror coating, for example with a layer of silver or of aluminum. However, instead, gold or a mixture of copper and aluminum may be applied by evaporation.
It is desired with the known lamp to direct the generated light for the major part to the exterior in directions remote from the neck-shaped wall portion. More particularly, it is desired to concentrate a largest possible fraction of this light with the mirror-coated wall portion. This object is achieved in that the light source of the lamp (a filament) is arranged in the immediate proximity of the focus of the parabolically curved wall portion and this focus is located deep in the parabolic portion near the neck-shaped wall portion. As a result, the focus is in fact enclosed by the parabolically curved wall portion over a larger spatial angle than when the focus with the same largest diameter of the lamp bulb is located, for example, on the largest diameter.
Electric lamps having a power value between 15 W and 100 W, for example of 15, 25, 40, 60, 75 and 100 W, intended to be operated at a standard voltage are manufactured in a large number of types. The finish, the coating or the processing of the lamp bulb wall, the shape of the lamp bulb and the shape of the inner parts of the lamp are different among the various types.
The following lamps are among the various types which are included in the above-mentioned power ranges:
lamps having a mirror-coated parabolically curved wall portion, opposite to which is located a window which, is glazed (is slightly light-scattering) due to an etching treatment and/or is coloured;
lamps having a substantially spherical lamp bulb which is transparent, or frosted, or which is coated with a white or coloured light-scattering layer;
lamps having a conical wall portion adjacent to and a curved wall portion opposite to the neck-shaped wall portion, the conical wall portion being provided with a white or colored light-scattering layer and the curved wall portion being slightly light-scattering and, as the case may be, being colored; these lamps emit light on all sides, but supply along the axis in directions remote from the neck-shaped wall portion a higher luminous flux than in other directions;
lamps having opposite to the neck-shaped wall portion a spherical wall portion, which is mirror-coated or is provided with a white light-scattering coating.
The manufacture of this large number of lamp types is very complicated due to the variety of bulb types, which require on the production machinery, with regard to shape and dimension, their own supply and lead-out mechanisms and transport means. The different lamp types also require different packaging. The readjustment of production machines from one lamp type to the other is thus a very laborious operation.